Greenhouse gas concentrations in the atmosphere have risen rapidly during the past two centuries.
Greenhouse gases in the atmosphere insulate our planet's surface against the chill of space, something known as the greenhouse effect.
The main greenhouse gases influenced directly and emitted by human activities are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and synthetic gases such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs).
Water vapour and ozone are also significant greenhouse gases, whose concentrations in the atmosphere are controlled mainly by the Earth's temperature and the emission of ozone producing chemicals, such as reactive hydrocarbons, and ozone destroying chemicals like CFCs.
Increased atmospheric concentrations
Global CO2, CH4, and N2O concentrations have risen rapidly during the past two centuries, which has enhanced the greenhouse effect and contributed to global warming.
The amount of these long-lived greenhouse gases in the atmosphere reached a new high in 2013. The concentration of CO2 in the atmosphere in 2013 was 395 parts per million (ppm) – much higher than the natural range of 170 to 300 ppm during the past 800 000 years.
The relative contributions to the enhanced greenhouse effect from pre-industrial times to 2013, due to the long-lived greenhouse gases, are: CO2 (64 per cent), CH4 (18 per cent), synthetics (12 per cent) and N2O (6 per cent).
Sources of greenhouse gas emissions
Global CO2 emissions are mostly from fossil fuels (more than 85 per cent), land use change, mainly associated with tropical deforestation (less than 10 per cent), and cement production and other industrial processes (about 4 per cent).
Energy generation continues to climb and is dominated by fossil fuels – suggesting emissions will grow for some time yet.
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